1. Field of the Invention
The present invention relates to a television cabinet for forming a casing of a television receiver.
2. Description of Related Art
A cabinet for forming a casing, for example, of a television receiver comprises a front enclosure to which a CRT or the like is mounted and a rear enclosure through which various kinds of terminals, for example, video or audio input/output terminals are passed. The front enclosure and the rear enclosure comprise a top plate, side plates and a bottom plate molded integrally.
FIGS. 3 and 4 show one example of a front enclosure. FIG. 3 is a front elevational view. FIG. 4 is a perspective view as viewed from the back. In the figures, are shown a front enclosure 30, a bottom plate 31, a top plate 32, side plates 33 and 34 and a front plate 35.
Below the front plate 35, are provided a speaker grill 37 for protecting a loud speaker, a control portion 38 having apertures disposed for various kinds of control keys (for example, for power on/off, channel up/down, volume up/down) or headphone terminals, and an opening 39 for attaching a loud speaker for a left hand voice channel in a case of a two-channel stereophonic television receiver. The opening 39 is adapted such that it may be covered by a predetermined lid in a case of a monaural television receiver, for example, or covered with a speaker grill of a shape symmetrical with the speaker grill 37 in a case of a stereophonic television receiver.
An injection trace 40 denotes a trace through which a resin is injected upon molding of the front enclosure 30. That is, the front enclosure 30 is molded integrally by injecting a resin from an injection port at a position of the injection trace 40 which is left after injection of the resin into a die, casting the resin as far as the end faces of the bottom plate 31, the top plate 32, and the side plates 33 and 34 and then removing the die.
As shown in FIG. 5, illustrating a partial cross sectional view along line C--C' of the top plate 32, the top plate 32 is molded such that the wall thickness d at the end face of the top plate 32 is made greater than the wall thickness c for a portion contiguous with the front panel 35 and a flow of the resin (for example, a polyester resin) is injected into the die upon molding. This is so adapted for lowering the pressure of the resin at the end face since the pressure of the resin injected from the injection port is in an inverse proportion to the cross sectional area of the die in which the resin flows.
That is, if the thickness d for the end face is made greater than the thickness c for the contiguous portion, the resin injected from the injection port can flow sufficiently as far as the top end of the die where the pressure is low, thereby molding the a front enclosure to a high accuracy.
Although not illustrated as a cross section, the thickness at the end face of the side plates 33 and 34 is made greater than the thickness d at the end face of the top plate 32, such that the thickness of the end faces of the side plates 33 and 34 is greater than the thickness for the contiguous portion of the front plate 35.
The contents of the above-mentioned technique are disclosed in the following three Japanese Patent Applications, i.e., Japanese Utility Model Laid Open Publication No. 02-046480, Japanese Patent Laid-Open Publication No. 62-292415 and Japanese Patent Laid-Open Publication No. 63-240469.
Incidentally, blow molding has been employed recently as a method of blowing the front enclosure 30 or the like. FIG. 6 schematically shows the outline of blow molding. In the figure, are shown a die 50, a cylinder 51 for injecting a resin J at a predetermined pressure to the die 50, a gas reservoir 52, a gas cylinder 53 having a piston P for compressing a gas G (for example, nitrogen) sent from the gas reservoir 52 and valves V1, V2 and V3 for controlling the gas flow. In the blow molding of the above-mentioned constitution, the resin J is injected in a previously calculated predetermined amount through an injection port 50a of the die 50 from the cylinder 51 and then the gas G is sent in the same manner after a predetermined delay from the injection port 50a to form a hollow structure.
At first, the gas G is injected into the gas cylinder 53 by opening the valve V1 and then the valve V1 is closed again. Then, the gas G is compressed by the piston P, and the valve V2 is opened at a predetermined timing. Then, the gas G forms predetermined hollow portions depending on the solidified state of the resin J and the wall thickness of the resin J injected into the die 50. Then, after the forming of the hollow portion, the gas valve V3 is opened to release the gas to the outside.
That is, by molding the hollow portion by the injection of the gas G, a structure of an increased thickness can be formed in specified regions which was difficult by usual molding and, for instance, a portion for mounting to support a CRT can be made more rigid, for example, in a case of the front enclosure 30.
However, in a case of using the blow molding method described above, if the thickness for the top plate 32 and the side plates 33 and 34 is not molded uniformly, only the flow of the resin J in the die 50 is considered. Then, if blow molding is conducted with such a wall thickness this will not provide constant resin pressure, the injected gas G will flow to a section with a larger thickness, that is, toward the end face at a lower resin pressure.
That is, the injected gas G cannot be controlled well and the gas G escaping from a section causes defects such as puncture from the inside to the surface of the front enclosure 30 or sink marks (hollow shape appearing on the surface by the gas G). Accordingly, this brings about a problem of reducing the strength of the front enclosure 30 and increasing the number of failed products.